In advance of design, permitting, and construction of a pipeline to deliver North Slope natural gas to out-of-state customers and Alaska communities, the Division of Geological & Geophysical Surveys (DGGS) has acquired lidar (Light Detection and Ranging) data along proposed pipeline routes, nearby areas of infrastructure, and regions where significant geologic hazards have been identified. Lidar data will serve multiple purposes, but have primarily been collected to (1) evaluate active faulting, slope instability, thaw settlement, erosion, and other engineering constraints along proposed pipeline routes, and (2) provide a base layer for the state-federal GIS database that will be used to evaluate permit applications and construction plans. The dataset represents all classified laser returns from the lidar survey and their associated geospatial coordinates.

Supplemental_Information:

This metadata file was written to document and describe, as a whole, all points classified as ground points generated for this project. For each data delivery area, reports documenting data collection methodology, accuracy, and quality control were provided by Watershed Sciences and the Oregon Department of Geology and Mineral Industries (DOGAMI). These reports have been combined into single comprehensive reports organized by delivery region. The lidar QC report (the comprehensive report from DOGAMI) and the lidar delivery report (the comprehensive report from Watershed Sciences) can be found at <http://dx.doi.org/10.14509/22722>. Information about the quadrangles included in individual delivery regions can be found in the lidar delivery index report included with the data download. The DGGS metadata standard extends the FGDC standard to also include several elements that are required to facilitate internal data management. These elements relate individual data items to a common dataset. This dataset describes a single layer titled:

all_points: classified laser returns from the lidar survey and their associated geospatial coordinates.

Planar coordinates are encoded using row and column
Abscissae (x-coordinates) are specified to the nearest 2.83
Ordinates (y-coordinates) are specified to the nearest 2.83
Planar coordinates are specified in meters

The horizontal datum used is North American Datum of 1983.
The ellipsoid used is Geodetic Reference System 80.
The semi-major axis of the ellipsoid used is 6378137.
The flattening of the ellipsoid used is 1/298.257222.

Data collection was was supported by funding from the Department of Natural Resources, Division of Geological & Geophysical Surveys (DGGS) and the Alaska Gas Pipeline Project Office and the Office of the Federal Coordinator. Lidar data was collected by Watershed Sciences, Inc., Corvallis, OR, Survey data was collected by McClintock Land Associates, Eagle River, AK, Quality control check for data was done by State of Oregon Department of Geology & Mineral Industries, Portland, OR.

Acquisition: The lidar data were collected between September and October 2010 and between May and July 2011. The survey used the Leica ALS60 system. Near-nadir scan angles were used to increase penetration of vegetation to ground surfaces. Ground-level GPS and aircraft IMU were collected during the flight.

Date: 2010 (process 2 of 4)

Processing lidar data: (1) Flight lines and data were reviewed to ensure complete coverage of the study area and positional accuracy of the laser points. (2) Laser point-return coordinates were computed using ALS Post Processor software, IPAS Pro GPS/INS software, and Waypoint GPS, based on independent data from the lidar system, IMU, and aircraft. (3) The raw lidar file was assembled into flight lines per return with each point having an associated x, y, and z coordinate. (4) Visual inspection of swath-to-swath laser point consistencies in the study area were used to perform manual refinements of system alignment. (5) Custom algorithms were designed to evaluate points between adjacent flight lines. Automated system alignment was computed based on randomly selected swath-to-swath accuracy measurements that consider elevation, slope, and intensities. Specifically, refinement in the combination of system pitch, roll, and yaw-offset parameters optimize internal consistency. (6) Noise (e.g., pits and birds) was filtered using ALS post-processing software, based on known elevation ranges, and included the removal of any cycle slips.

Date: 2010 (process 3 of 4)

Lidar data points were classified through automated point processing algorithms and manual inspection. See the lidar delivery report for details regarding classification of lidar data points.

Data sources used in this process:

ASPRS, 2008

Date: 2012 (process 4 of 4)

A metadata file has been written to document and describe, as a whole, the entirety of the all point files generated for this project.

Absolute accuracy refers to the mean vertical offset of lidar laser point data relative to measured ground-control points (GCP) obtained throughout the lidar sampling area. The contractor used a surveying system to measure GCP's. GPS survey techniques allow surveyors to collect many precisely located GCP's which can be used as a control comparison with lidar elevations. A licensed surveyor is often able to post process GPS survey data to accuracies less than 1 cm both horizontally and vertically. Lidar 1 m grids were loaded into ArcGIS software for visual analysis. Data were examined through slope and hillshade models of bare earth returns. Both bare earth and highest hit models were examined for calibration offsets, tiling artifacts, seam line offsets, pits and birds. Please see the lidar delivery report and the lidar QC report for specific information about laser point processing and accuracy evaluation.

Horizontal accuracy refers to the ability to place laser points from multiple flight lines in the same location. Horizontal accuracy is measured as the divergence between points from overlapping flight lines. Accuracy is affected by system attitude offsets, scale and GPS/IMU drift. Manual system calibration and automated attitude calibration techniques were used to resolve divergence of data. Please see the lidar QC report and lidar delivery report for specific information about accuracy of lidar data.

Vertical accuracy refers to the elevation difference between measured GPS control data and lidar bare-earth digital elevation models. Project specifications require the root mean square vertical offset to be less than 0.2 meters. Please see the lidar QC report and lidar delivery report for specific information about accuracy and quality of lidar data, including a comparison of GCP elevations with bare-earth digital elevation model elevations.

Lidar returns have been examined to ensure that data from overlapping flight lines have consistent elevation values. Project specifications require that lidar consistency, measured as vertical offsets of data between adjacent flight lines, must average less than 0.15 meters. Flight lines have been examined to ensure that there was at least 60% sidelap and that there are no data gaps. All file naming conventions and formats have been checked for consistency. Refer to the lidar QC report and the lidar delivery report for statistics from consistency analyses of individual delivery sets.

The dataset(s) is (are) available directly from the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (see contact information below).

Use_Constraints:

Any hard copies or published datasets utilizing these datasets shall clearly indicate their source. If the user has modified the data in any way, the user is obligated to describe the types of modifications the user has made. The user specifically agrees not to misrepresent these datasets, nor to imply that changes made by the user were approved by the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys. The State of Alaska makes no express or implied warranties (including warranties for merchantability and fitness) with respect to the character, functions, or capabilities of the electronic data or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity whether from the use of the electronic services or products or any failure thereof or otherwise. In no event will the State of Alaska's liability to the Requestor or anyone else exceed the fee paid for the electronic service or product.

The State of Alaska makes no express or implied warranties (including warranties of merchantability and fitness) with respect to the character, function, or capabilities of the electronic services or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity whether from the use of the electronic services or products, any failure thereof, or otherwise, and in no event will the State of Alaska's liability to the requester or anyone else exceed the fee paid for the electronic service or product.

DGGS is developing options to make the data available to users directly from the internet; however, it is currently only available via hard drive. There are two options for copying the data to a hard drive: (1) DGGS will purchase a brand-new, 2 TB hard drive that you will be billed for when the data is picked up or sent, OR (2) you may provide a new, unopened* (in original packaging, including shrink-wrap - *The State of Alaska IT security policy prohibits non-State resources from being connected to a State of Alaska network. Thus, only unused drives can be used.) 2 TB or larger hard drive. Upon release, the complete set of point-cloud data will be available to users in LAS 1.2 format. The point-cloud files total approximately 1.2 TB. The data will be copied onto the drive in gzip (gz) file format. DGGS recommends uncompressing this data using 7-Zip, a free program available from <http://www.7zip.org>. For all orders, please include: title and publication number.